I'm building an 1991 RX-7 FC S5 race car and the car is completely gutted and I created a wiring harness from scratch. All of the emissions equipment is removed from the engine and the engine starts and idles fine. The problem is if I try to give it any throttle under load or hit the pedal fast, the engine back fires and lays flat. I can rev up the engine to redline, but only if I go very slow and any quick input makes the engine makes the engine almost die. Also, I have my VDI/6PI wired open since I will not need low end torque.

What have I tested and tried?

* Swapped AFM
* Swapped pressure sensor
* Replaced all vacuum lines (almost none due to it being a race car)
* Tested voltage at ECU and at sensors of every input/output and they are within FSM specs.
* Checked for vacuum leaks
* Replaced fuel filter
* Swapped entire throttle body
* Swapped secondary injector rail and injectors
* Eliminated fuel pump relay and resistor (wired on or off by toggle switch)

I would imagine if it was the throttle position sensor that needed adjusting that it wouldn't do the exact same thing with another known good throttle body + attached throttle position sensor.

What I need need to check:

* Fuel pressure
* Flow testing of all injectors

For the problem to be so apparent and not changing at all with replacing all of the parts above and all of the sensors reading fine, it has to probably be a sub system that is critical to the engine. My guess is fuel pressure at this point, but before I built the car there was no problem with the fuel pump.

Any ideas on what I should check next?

 

I just checked fuel pressure and it is 38 psi at idle and that looks perfectly fine. So, I know it is getting fuel and the AFM seems to be functioning. Should the injector wires be insulated for EMF?

 

Timing, and are your trailing plugs even firing?

 

Ahhh! You could be right. I checked and all the plugs are firing and the spark is really strong on all 4 plugs. What I did noticed is that if I unplug any of the leading plugs, you can tell it is running worse. If I unplug any of the trailing plugs, I don't notice anything different. The trailing plugs are firing fine, but could it just be that the timing is off?

I haven't checked the timing yet so this very well could be it. Thoughts?

 

Ok, here is where I am at. I aligned the pulley to the yellow mark, pulled the CAS, align the pin with the notch, reinstalled the CAS, set the timing on L1 to the yellow dot at idle. I switched over to T1 and the yellow dot was still lined up with the pin. There is not enough adjustment to get the red dot to even line up. This sounds pretty wrong as it seems that the red dot should line up on T1 and the yellow dot should line up on L1. Does this sound like a wiring problem with my trailing coil?

 

Sounds like you have your L1 and T1's mixed up. Are you ABSOLUTELY sure that you have the spark plug wires connected to the proper locations on both the coils and engine. Because from what you said, you can connect the timing light to L1 and the eccentric shaft pulley yellow mark lines up with the front cover pointer. Then, you move it directly over to T1 and it still shows the yellow mark lined up with the front cover pointer again. That's weird.

 

Here is where I am at now. I pulled the CAS, aligned the marks, rotated the crank to the needle and yellow mark line up, attached timing line to L1, adjusted CAS to move yellow mark to needle, attached to T1 and the red dot is slightly advance, say 1-2mm from the needle. Since there is only one adjustment, that is about as good as I can do. I think the red mark being close should be good enough. That didn't fix the choking and backfiring problem as soon as engine sees load.

Next steps:

* Disconnect secondary injectors and verify the problem still exists at low RPMs.
* Check and swap out primary injectors.
* Use a scope and monitor all 4 injectors cycles with RPMs

I'm pretty sure I'm getting a rich condition given that the plugs are brand new and they are completely black and the detonation in the exhaust. I think I'm getting too much fuel for some reason.

 

Ok, I'm still out of luck and I have tested a whole bunch of more things.

This is what I have done next and still the same problem:

* Swapped ECUs
* Disconnected secondary injectors
* Reversed primary injector wires (in case I wired them up backward)
* Checked compression: 100psi on both rotors
* Swapped trailing coil

I'm going nuts with this one. The only thing I haven't done is swapped the primary injectors and I'm pretty sure it is going rich and dumping fuel when you immediately push the pedal.

 

This is everything I have verified:

* Swapped AFM
* Swapped pressure sensor
* Replaced all vacuum lines (almost none due to it being a race car)
* Tested voltage at ECU and at sensors of every input/output and they are within FSM specs.
* Checked for vacuum leaks
* Replaced fuel filter
* Swapped entire throttle body
* Swapped secondary injector rail and injectors
* Eliminated fuel pump relay and resistor (wired on or off by toggle switch)
* Swapped ECUs
* Disconnected secondary injectors
* Reversed primary injector wires (in case I wired them up backward)
* Checked compression: 100psi on both rotors
* Swapped trailing coil
* Verified fuel pressure: 38psi

I'm running out of ideas to test.

One new idea: Do I have to insulate each of the 3 crank sensor wires that run to the ECU or can I insulate all of them together in one sleeve? I have all 3 wires in one EMF sleeve and I think that should be fine.

 

* Reversed primary injector wires (in case I wired them up backward
It wouldn't matter if the 2 primary injectors were switched with each other.tThey fire at the same time.
.BUT have you tried switchin the primaryinjector wires with the secondary?
Why?:
I went through a similar scenario and after THREE months of sheer Lunacy that is what it was..I had the Wiring mixed up.(Primaries were wired as secondaries and Secondaries were wired as Primary).
touch the gas and it Dies.,bogs Farts Backfires..

 

I already checked that by checking continuity between the leading and trailing coil wired..

Something just dawned on it that I can't believe no one noticed....

I deleted the OMP all together and I'm running the stock ECU. Isn't very possible that the engine is going in limp mode because it doesn't see the OMP? This seems VERY possible.

 

LOL! I think you just answered your own question. You would have s CEL come on, but I'm guessing you took out the idiot lights.

Time for a standalone, or you can go cheap and get an RTek chip installed in the stock ECU.

 

Yeah, I laughing at myself last night and there is no way I could have known because I don't have any of the idiot lights and no easy way to check engine codes.

I've read mixed advice on the OMP delete. Some say just wire it into the harness and you don't need it connected to the engine and other people say you need to have it on the engine because the ECU reads its movement and decide if it is going to make the engine go limp.